The provision of presence services is set to become an important feature of third generation IMS (IP Multimedia Core Network Subsystem) mobile communication systems. A presence service utilises a server to accept information, store it, and distribute it. The information stored may for example relate to a user's willingness to communicate or their capability for communication, or it may be general information relating to the users, or graphics data. The service offers users the opportunity to receive status information relating to one or more other user(s). Presence services also allow applications and services to be provided to a user of mobile or fixed equipment in dependence on the position or location of the user or equipment. Presence services also facilitate instant messaging (IM).
In mobile communication systems it is important to minimise the traffic over the radio interface. In known proposals for implementing presence services, when a user subscribes to presence services the presence server transmits all possible presence information for the user over the radio interface to the user's terminal. Thus all the presence data that is available is first provided to the user, and after that the user optionally selects the data of interest. This procedure places an unnecessary burden on the radio interface in a wireless environment, as unnecessary data traffic which is not needed by the user is transmitted over the radio interface. It is also possible that the receiving terminal may not be able to store and handle all the presence data which is transmitted to it by the presence server.
In current known proposals, all of the presence data is transmitted to the user terminal for “learning” purposes, i.e. so that the user can select what information is of interest based on knowledge of what information is available.
A further known proposal relates specifically to the presence and instant messaging architecture. The proposal is to utilise the SUBSCRIBE message, which is a SIP (session initiation protocol) message, for a presence client to specify that it wishes to receive notification of events occurring at an application server or known to the application server. In the case of a presence server, the event may be that a presence entity (known as a presentity) has become available, for example, for instant messaging.
The conditions under which a client is notified of an event are defined by the presence service and controlled solely by the application server. In addition, however, a client may cancel their own subscription. Typically presence applications specify that a client is notified whenever a status changes.
It has been proposed that a client may specify their own notification rules for their subscription. For example, the rules may be specified in the body of the SUBSCRIBE request message, using a formal description language such as SOAP (Simple Object Access Protocol) or XML (extended mark-up language). Upon receipt of the subscription, the application server, such as a presence server, validates the notification rules and applies them to the subscription. When the client-specified rules are enabled, an appropriate notification is sent to the client. The effect of the rules is thus to enable a client to specify the conditions as to when it should be notified and what content should be delivered (e.g. only attributes of interest)
The application of such a client-defined filter applied at the application server has the advantage of reducing communications from the application server to the client, and thereby minimising bandwidth load on the communication link from the application server to the client and processing (interrupt handling) at the subscriber unit.
However, such an arrangement potentially has a drawback in that it relies upon a client which has the capability to define a set of filter rules, and an application server which has the ability to interpret and apply such rules. If either the client or the application server does not have the appropriate capability, then the filter arrangement cannot work. Event notification applications, such as presence servers, may not have the functionality to include the necessary capabilities, especially legacy applications which may require undesired upgrades. Alternatively, a service provider may not wish to provide such capability. The support of filtering to every application server subscribed to by a client requesting such filtering is onerous. Thus the usefulness of such filtering is severely limited.
It is an object of the present invention to provide an improved method for providing access to application services, which addresses one or all of the above-stated problems.